A cough after a viral infection can persist for three weeks and that is entirely normal. Beyond that, it stops being a leftover from a cold and starts being a symptom in its own right.
In India, a cough lasting more than two to three weeks carries a specific obligation to exclude tuberculosis.
Classifying by Duration
Duration narrows the diagnosis more than any other feature.
- Acute, under 3 weeks: usually viral infection, and resolves
- Subacute, 3 to 8 weeks: most commonly post infectious, but tuberculosis must be considered
- Chronic, over 8 weeks: requires systematic investigation
Post viral cough is genuinely common and can persist for six to eight weeks as the airway lining recovers. It is dry, gradually improving, and comes with no other symptoms. That pattern is reassuring where TB has been excluded.
Tuberculosis Must Be Excluded
India carries a large share of the global tuberculosis burden, and delayed diagnosis both harms the patient and spreads infection.
- Cough for two weeks or more, particularly with sputum
- Fever, characteristically in the evenings
- Drenching night sweats
- Unintentional weight loss
- Loss of appetite
- Coughing up blood
- Contact with a known TB case
Testing involves sputum examination, ideally with a rapid molecular test which also detects drug resistance, alongside a chest X ray.
TB is curable with a complete course of treatment. The critical issue is completing it. Stopping early because symptoms improve is the main driver of drug resistant TB, which is far harder and more expensive to treat.
The Three Most Common Causes of Chronic Cough
In non smokers with a normal chest X ray, three conditions account for the large majority.
Upper airway cough syndrome, previously called post nasal drip. Throat clearing, a sensation of mucus dripping, worse on waking. Related to rhinitis or sinusitis, and treated with nasal steroid spray and saline irrigation.
Asthma, including cough variant asthma. Cough worse at night and early morning, triggered by exercise, cold air, dust or laughing, often with no wheeze at all. This is frequently missed, and cough may be the only symptom.
Reflux. Cough after meals or lying down, often without any heartburn. Treated with lifestyle measures and acid suppression, though improvement takes two to three months.
These three can coexist, which is why a partial response to treatment for one does not exclude the others.
Other Causes Worth Considering
Several additional causes appear regularly.
- ACE inhibitor cough: a dry persistent cough from a common blood pressure drug class, occurring in a notable proportion of users. It can begin months after starting the drug, so patients do not connect the two. It resolves within weeks of switching
- COPD: in smokers and in people exposed to biomass cooking smoke, which is a significant cause in Indian women
- Bronchiectasis: chronic productive cough with large volumes of sputum, often following childhood infection
- Whooping cough: occurs in adults with waning immunity, causing prolonged paroxysmal cough
- Lung cancer: particularly in smokers, or with a change in a long standing cough
- Heart failure: cough with breathlessness and ankle swelling
- Interstitial lung disease: dry cough with progressive breathlessness
The ACE inhibitor cough is worth checking first in anyone on blood pressure treatment, since stopping the drug is a simple diagnostic test.
Red Flags Requiring Prompt Investigation
These features warrant urgent assessment rather than a trial of treatment.
- Coughing up blood
- Unexplained weight loss
- Persistent fever or night sweats
- Progressive breathlessness
- Chest pain
- Hoarseness lasting more than three weeks
- Difficulty swallowing
- A smoking history with a change in an existing cough
- Finger clubbing
Coughing up blood always requires investigation, even a small amount and even once. Our pulmonology department assesses these promptly.
The Investigations
Assessment is stepwise rather than doing everything at once.
- Chest X ray: first line for any cough over three weeks
- Sputum for TB, including molecular testing
- Spirometry: lung function testing, with reversibility testing for asthma
- Blood tests: full blood count, inflammatory markers, eosinophil count
- CT chest: where the X ray is abnormal or symptoms persist unexplained
- Bronchoscopy: for suspected malignancy, unexplained bleeding or persistent unexplained findings
A normal chest X ray does not exclude asthma, reflux or post nasal drip, which are diagnosed clinically and by response to treatment rather than by imaging.
Cough Syrups Do Little
Over the counter cough preparations have limited evidence and are widely overused.
Suppressants may help a dry cough disturbing sleep in the short term. Expectorants have little proven benefit. Combination syrups containing multiple ingredients often include sedating antihistamines and are not appropriate for prolonged use, particularly in children.
Codeine containing preparations carry dependence risk and should not be used long term.
Simple measures often work as well: honey in warm water, which has reasonable evidence in children over one year, steam inhalation, adequate hydration, and avoiding irritants including smoke.
The productive approach is to treat the cause rather than suppress the symptom.
What You Can Do Now
Before your appointment, gather information that will speed the diagnosis.
- Note how long the cough has lasted and whether it is improving
- Note whether it is dry or productive, and the colour and amount of sputum
- Note timing: night, early morning, after meals, with exercise
- List all medications, particularly blood pressure drugs
- Note any weight loss, fever or night sweats
- Note exposure to smoke, dust or cooking fumes
- Note any contact with someone with TB
- Stop smoking, which is both diagnostic and therapeutic
Cooking smoke exposure deserves specific mention. Chronic biomass fuel exposure is a major cause of respiratory disease in Indian women who have never smoked.
A cough lasting over three weeks needs a chest X ray and TB testing, particularly with fever, night sweats or weight loss. In non smokers with a clear X ray, the answer is usually asthma, reflux or post nasal drip, all of which respond well once identified.
Our pulmonology and general medicine departments at T. Nagar assess persistent cough.
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